Aqueous solutions of alkali polysilicates

Abstract

A process for the preparation of an aqueous alkali metal polysilicate solution having an SiO 2 : alkali metal oxide mole ratio of 2.5 - 5.5 : 1 and a silica content of 16 - 23% by weight which comprises contacting a tetraalkoxysilane of the formula Si(OR) 4 wherein each R is independently a straight or branched-chain alkyl group of 1 to 3 carbon atoms with an aqueous alkali metal hydroxide solution at a temperature between room temperature and the boiling point of the reaction mixture and at a temperature up to 100° C. distilling over alcohol formed by the reaction of the silane with the alkali metal hydroxide.

What is claimed is: 
     
       1. A stable aqueous lithium polysilicate solution of a lithium polysilicate, said solution containing alkoxy groups of 1 to 3 carbon atoms, said solution having less than 50 parts per million of sodium or potassium ions wherein the mol ratio of silica to lithium oxide is 4-5:1, the SiO 2  content of said solution is between 20 and 22 percent by weight, said stable aqueous lithium polysilicate solution prepared by a process consisting essentially of contacting a tetraalkoxysilane of the formula Si(OR) 4  wherein each R is independently a straight or branched-chain alkyl group of 1 to 3 carbon atoms with an agent consisting essentially of an aqueous lithium hydroxide solution at a temperature between room temperature and the boiling point of the reaction mixture and at a temperature up to 100° C., the ratio of silane to lithium hydroxide being such that the reaction product has a silica to lithium oxide mol ratio of 4-5:1, distilling over substantially all of the alcohol formed by the reaction of the silane with the lithium hydroxide down to a residual alkoxy group content of 0.15 to less than 2 weight percent and during or immediately following said distillation adding water to adjust the silica content of said solution to between 20 and 22 weight percent and cooling the resultant product with stirring. 
     
     
       2. An aqueous lithium polysilicate solution according to claim 1 wherein the alkoxy groups of the polysilicate are methoxy groups and the methoxy group content of the solution is less than 2 percent by weight. 
     
     
       3. An aqueous lithium polysilicate solution according to claim 1 wherein the alkoxy groups of the polysilicate are methoxy groups and the methoxy group content of the solution is 0.15 percent by weight. 
     
     
       4. An aqueous lithium polysilicate solution according to claim 1 wherein the alkoxy groups of the polysilicate are methoxy groups and the methoxy group content of the solution is about 1.5 percent by weight. 
     
     
       5. An aqueous lithium polysilicate solution according to claim 1 wherein the alkoxy groups of the polysilicate are ethoxy groups and the ethoxy group content of the solution is about 1.1 percent by weight.